Recently, there has been a concentrated research effort in the field of monocyclic .beta.-lactam antibiotics. Discoveries of antibacterial agents have included 3-acylamino-2-azetidinones having in the 1-position a (i) sulfonic acid salt substitutent (see, for example, United Kingdom Pat. No. 2,071,650, published Sept. 23, 1981); (ii) [(substituted sulfonyl)amino]carbonyl substituent (see European patent application No. 62,876, published Oct. 20, 1982); (iii) phosphinic or phosphonic acid substituent (see European patent application No. 61,765, published Oct. 6, 1982); and (iv) (acylamino)sulfonyl substituent (see United Kingdom Pat. No. 2,104,069, published Mar. 2, 1983). These .beta.-lactams can be represented by the structural formula ##STR5## (optionally substituted in the 4-position) wherein X is one of the activating groups described above.
Various processes are described in the cited references for preparing .beta.-lactams of the above structural formula. One such method involves the addition of the activating group ("X") to the corresponding .beta.-lactam having the formula ##STR6## (optionally substituted in the 4-position).